The detection of small particles, e.g. particles having sizes of less than 100 nm, has been drawing considerable interest in recent years. Such particle detection is for instance of interest in the field of nanotechnology, where the detection of the size of such particles can provide relevant information about for instance the particle manufacturing process or about the applicability of the particles for a predetermined purpose. Another application domain where the detection of small particles has become of interest is the medical field, where for instance the detection of e.g. viruses in a fluid such as the human blood can aid the detection of certain diseases in early stages, e.g. prior to the patient demonstrating symptoms indicative of the disease, thus increasing the chance of successful treatment. Other particles that may be detected include polymer molecules, proteins and so on.
In the particle detection field, optical systems are especially attracting interest due to the high resolution of such systems, thereby allowing the detection of very small particles. An example of such a particle detection system is disclosed in US2007/0030492 A1, which uses an interferometric approach by means of detecting the phase difference between a reference beam of electromagnetic radiation and a beam of the same radiation projected through a flow cell. The light scattering caused by the particles in the flow cell causes the reflection of electromagnetic radiation back to a detector, where the phase difference between the backscattered radiation and the reference beam is determined. A drawback of this system is that the particle size resolution is limited to particles having a size of several nanometers. Moreover, the system is relatively large and, as a consequence, relatively costly.